In copending parent patent application Ser. No. 07/906,573, filed Jun. 30, 1992, small articles such as dry cell batteries, lipstick containers, lip balm containers and the like are labeled with high quality, thin film polymeric labels. Labels are fed to a label transport drum, which includes a fixed, cylindrically configured hub, and a cylindrically configured drum rotatably mounted on the hub. The drum has an outer surface on which labels are fed as a strip, and moved with the drum through a label drag area where the label strip is cut into labels of predetermined size.
As the label moves with the rotating drum, an adhesive is printed onto the area adjacent the leading edge of the label and a predetermined amount of solvent is evenly wiped onto the area adjacent the trailing edge of the label so as to dissolve partially the surface of the label and form a tacky bond. The label moves to an article wrapping position where the articles, such as dry cell batteries, are wrapped, securing first the leading edge to the article, followed by overlapping the trailing edge onto the leading edge so that the trailing edge solvent creates a solvent-seal bond. The labels are then heat shrunk over the articles. The apparatus provides for high quality cylindrical labeling of small articles such as dry cell batteries using thin film, polymeric labels, e.g., typically less than 0.0035 inches thickness.
As disclosed in the copending, parent application, new and surprising results are obtained in solvent application when a speed differential is produced between a rotating, flexible wiper tip and a label moving on the label transport drum. The speed differential between the wiper tip and the label causes application of a "bead" of solvent at the point of departure of the wiper from the label, at a point adjacent to, but spaced from the trailing edge of the label. If the wiper is moving slower than the surface speed of the label transport drum, the solvent is wiped toward the trailing edge of the label. If the wiper is moving faster than the surface speed of the label transport drum, the solvent is wiped from the trailing edge forward. As the article rolls back over the solvent during wrapping, the weight of the article pushes the solvent evenly across the pretreated area of the trailing edge on which the solvent was applied, thus in essence obtaining a more even solvent wipe along the trailing edge of the label.
Typically, the applied solvent, such as THF or other similar solvents, is more viscous than water. As the wiper tip rotates at high operating speeds, the solvent sometimes may splash onto the area adjacent the trailing edge of the label giving a mottled appearance to the trailing edge and forming a poor seam between overlapping portions of the label. It is therefore desirable to apply the solvent by a means other than a rotating wiper.
Additionally, as disclosed in the parent application, the wiper engages a gravure roller. The gravure roller receives solvent from another solvent pad or a solvent dip bath. This system has three or more transfer points which may create inaccuracies and imprecise solvent transfer.
A static wiper positioned adjacent the peripheral drum surface would eliminate splashing caused by rotation and reduce the number of transfer points. A static wiper, however, is fixed adjacent the drum surface, and unless some means is provided for biasing the trailing edge outward from the drum surface, the static wiper would not adequately engage the trailing edge of the label for solvent transfer.
U.S. Pat. No. 4,844,760 to Dickey discloses a static wiper and a fixed protrusion on the surface of a label transport drum which spaces the trailing edge of the label outward from the periphery of the drum so that the trailing edge engages the wiper tip. However, if smaller articles are used such as dry cell batteries, the article would roll up and over the protrusion, resulting in poor quality wrapping. It has been found that any protrusion that moves the trailing edge outward should also move inward during article wrapping to prevent interference between the article, the label and the drum surface.
Also, it has been found that labels sometimes are unclean and contain contaminants on the surface which cause 1) poor solvent application, 2) poor solvent penetration resulting in mottling, and 3) poor seam quality and wrap quality. It is therefore desirable to clean the trailing edge of the label before sufficient solvent is applied onto the label for complete solvent penetration and solvent-seal bonding. Additionally, the cleaning step should act as a pretreating step, softening the label in preparation for complete solvent application and penetration. Such requirement will also mandate precise metering of solvent.